Just visited Cuba for a few days. (46 minute flite from FLL -Miami area).
Cuba has almost no wifi. It is a POOR country. No cell phone stores I saw, altho there is cell service available, to some extent.
Altho TMobile US has free intl roaming in 140+ countries, Cuba isn't one of them. Incoming/outgoing calls $2/min, 50 cents outgoing text (incoming free) and $2/mb for data.
Went thru total wifi/cell withdrawal for 5 days!

Upon return - learned that Digicel sells a prepaid card for roaming in Cuba. $25 for 100mb of data. They have other offers as well.CubaRoamingHelp@digicelgroup.com or call 1-407-499-2822.

Also sold on Amazon.

Make use of T-M's UMA/wifi free calling from any place in the world with access to wifi. I use an LG G6, wife an S7)
A/o Oct 20, 2013 no need for intl prepaid as T-Mobile U.S. includes voice roaming at 20¢/min (in and out)., unlimited text (in and out), and unlimited data in 140+ countries.

My Plan -[6 lines] U.S. T-Mobile unlimited minutes (incoming and outgoing), unlimited text, fast data on each line. that $145/mo. total! . (In U.S. no surcharge for calling a cell.) If a line exceeds 2G of data in a month, pay $10 more for that line. [That only happens a couple times/year.